This proposal requests funds to purchase a liquid chromatograph mass spectrometer (LC-MS) to support the research of five major users (all NIH funded) and two minor users (one NIH funded). All major and minor users are faculty in the chemistry and biochemistry department at the University of Delaware. The instrument will be placed in an open- access laboratory under the supervision of the departmental mass spectrometry facility. Walk-in users will be able to choose one of several pre-established methods that are designed for fast sample turn around. More sophisticated experiments will be performed with assistance from personnel in the mass spectrometry facility and will be scheduled in a manner that minimizes the impact upon walk-in use. The proposed LC-MS instrument will facilitate several ongoing research projects. These projects include: (Colman) characterization of new affinity labels, chemically modified enzymes and purified modified peptides and mutant enzymes; (Koh) selective regulation of gene expression with small molecules and light activated gene expression for temporal and spatial control of gene expression; (Mueller) enzymology of RNA modification, pseudouridine synthases and 4-thiouridine generation; (Riordan) model studies of acetyl coenzyme A synthase; (Thorpe) flavoproteins in fatty acid metabolism, acyl coenzyme A dehydrogenases and related enzymes of fatty acid beta-oxidation, and sulfhydryl oxidase catalysis.